The present invention relates to an apparatus for scattering particles, in particular particles admixed with at least one binder, such as, for example, fibers, chips or like particles containing ligno-cellulose and/or cellulose, to form a mat, in particular for manufacturing shaped articles, primarily in the form of boards, having at least one metering hopper containing the particles, having at least one scattering station for the particles positioned after the metering hopper and having a forming band to receive the mat arranged underneath the scattering station. Furthermore, the invention is directed to a method for the manufacture of chip/fiber combination boards comprising in each case two cover layers formed from fibers admixed with at least one binder and an intermediate layer arranged between the cover layers and formed from chips admixed with at least one binder, in particular for the operation of a corresponding apparatus, and to a corresponding chip/fiber combination board. Finally, the subject of the invention is also an apparatus and a method for scattering particles to form a mat of variable width.
Apparatuses for scattering mats are known in a number of variants, with these apparatuses usually being specifically adapted in each case to the end product to be manufactured, for example to the kind of board to be manufactured (fiberboard, chipboard or chip/fiber combination board) and to a respective fixed width of the mat to be scattered. A change in manufacture from one product kind to another product kind and from one mat width to another mat width requires a relatively time-consuming conversion of the plant, plant downtimes associated therewith and relatively high costs.
It is an object of the invention to provide an apparatus and a method of the kind initially mentioned which allow in a very variable manner the manufacture of different kinds of product, i.e. alternatively chipboard, fiberboard or chip/fiber combination boards or boards with different widths at an economically justifiable effort and cost.
This object is satisfied in accordance with the invention by the features of the claims. A chip/fiber combination board in accordance with the invention is characterized by the features of the claims.
The apparatus in accordance with the invention according to claim 1 allows both the manufacture of single-layer or multi-layer chipboards or fiberboards and of chip/fiber combination boards without any time-consuming and costly conversion of the apparatus being required. The chip/fiber combination boards which can be produced with this apparatus moreover have a very high strength and optimum surface properties, with, at the same time, the cover layers consisting of fibers or chips having a relatively thin form. These advantages are achieved by the chip scattering station formed to scatter the intermediate layer comprising a fractionating device for the separation of fine and coarse chips, with the fine chips being scattered as the outer layers of the intermediate layer and the coarse chips being scattered as the inner layer of the intermediate layer. It is achieved in this way that the fine fibers of the cover layers do not come into contact with the coarse chips, but with the fine chips of the intermediate layer, whereby a substantially better connection is achieved between the cover layers and the intermediate layer.
The fine chips lying at the outsides of the intermediate layer furthermore form a buffer zone in each case between the fibers forming the cover layer and the coarse chips forming the core. This buffer zone prevents the coarse structure of the coarse chips pressing through the cover layers consisting of fibers, whereby the surface of the boards produced from the mat would receive an unwanted roughness. This so-called xe2x80x9ctelegraphingxe2x80x9d of the coarse chips to the outside of the boards is thus prevented in chip/fiber combination boards manufactured with the apparatus in accordance with the invention.
The same advantages are achieved in accordance with the method of the invention, since the chip/fiber combination boards manufactured in accordance with this method have, on the one hand, a particularly high strength due to the increased connection between the cover layers and the intermediate layer and, on the other hand, optimum surfaces due to the prevented telegraphic effect. The chip/fiber combination boards obtained in this manner have a very compact surface which is, for example, ideally suited for lacquering since the required lacquer quantity can be reduced due to the compact surface.
The apparatus formed in accordance with the invention is, however, also suitable for producing pure chipboards and pure fiberboards in addition to producing chip/fiber combination boards, with both single-layer and multi-layer chip/fiber boards being able to be produced. If only chipboards are to be produced, the fiber scattering stations are switched off so that a mat is scattered onto the forming band only from the chip scattering station. The scattered mat can then have, for example, an intermediate layer consisting of coarse chips and two outer cover layers consisting of fine chips. However, it is also possible to load the fractionating device exclusively with homogeneous chips so that a single-layer chip mat can be scattered
If only single-layer or multi-layer fiberboards are to be produced, then the chip scattering station can be deactivated accordingly so that only a mat consisting of fibers is scattered onto the forming band. Only one of the fiber scattering stations or both scattering stations can then be activated depending on the desired thickness of this mat.
The fiber scattering stations are advantageously designed to scatter homogeneous fiber material, since the apparatus in accordance with the invention can be simplified in this way. Since a fractionating of the chips is carried out at the time the intermediate layer consisting of these chips is formed, so that the fine chips come to rest at the outside of the intermediate layer, the optimum connection between the intermediate layer and the cover layers can be produced by this fractionating so that a corresponding fractionating of the fibers forming the cover layers becomes superfluous.
To allow the alternative manufacture of chipboards, fiberboards or chip/fiber combination boards, the scattering stations can be controllable independently from one another. Furthermore, each scattering station can have its own metering hopper associated with it; or a common metering hopper can be associated with at least a part of the fiber scattering stations, in particular all fiber scattering stations. The use of a common metering hopper ensures that cover layers scattered from the fiber scattering stations are each loaded with the same homogeneous fiber material.
In accordance with a further advantageous embodiment of the invention, the scattering stations are formed separately from one another. This modular construction means that standard scattering stations can be used so that the costs of a corresponding apparatus formed in accordance with the invention can be reduced.
The apparatus formed in accordance with the invention can have both a continuous press and a synchronized press downstream to press the scattered mat, with the pressing of the mat usually taking place with the simultaneous supply of heat, with a pre-heating of the mat additionally being able to be carried out in particular directly prior to the downstream pressing apparatus and a pre-pressing of, for example, the part mat scattered by the fiber scattering station arranged at the entry side being carried out.
It is possible with an apparatus as disclosed to scatter mats of different widths without, for example, having to provide conveyor belts or scattering devices of varying widths. Such an apparatus is operated particularly advantageously in accordance with the disclosed method.
Since the particles are initially scattered onto the forming band in a normal, full-area manner from a scattering station, i.e. with the maximum width given by the scattering station, a standard scattering station can be used without any alterations having to be made to it. Only the mat arranged on the forming band in its full width is reduced to the desired width by the particle separating device provided at the top side of the forming band, with the excess particles being carried off to the side. Mats of any width can thus be produced using standard scattering stations and standard conveyor belts due to the adjustability of the particle separating device.
To achieve a symmetrical arrangement of the mat on the forming band, the particle separating device comprises preferably two part units arranged symmetrically to the longitudinal axis of the forming band. These can be formed, for example, as rotating separating units with which the particles forming the marginal regions of the mat can be transported off to the side. The part units can, for example, also be formed as separating walls which extend at least regionally substantially parallel to the direction of movement of the forming band and which are aligned substantially perpendicular to the forming band. The width of the scattered mat can be reduced to the desired width by an adjustment of the rotating separating units or separating walls in the horizontal direction, in particular transversely to the forming band. The particles led off to the side by the particle separating device can then be fed back to the metering hopper of the scattering device so that they are available for the further scattering procedure.
If a plurality of scattering stations are connected one after the other to produce multi-layer mats, then the mat initially scattered at maximum width from the first scattering station can be reduced to the desired width, for example, by rotating separating units, with the particles separated by the separating units being fed back to the metering hopper of the first scattering station. The mat reduced in width in this way is conveyed on the forming band to the next scattering station where it is guided, for example, between two separating walls prior to reaching the scattering region. These separating walls extend over the whole length of the second scattering station so that the particles also scattered at maximum width by this second scattering station come to rest in part on the part mat scattered from the first scattering station within the separating walls and in part directly on the forming band outside the separating walls. Since a mixture of particles of the first scattering station and the second scattering station is prevented outside the separating walls in this way, the particles outside the separating walls can, after passing the second scattering station, also be carried off to the side by separating units and fed back to the metering hopper of the second scattering station.
After this leading off to the side of the excess particles, a two-layer mat of the desired reduced width is thus present on the forming band and this mat can be conveyed with or without separating walls to a further scattering station or to a pressing apparatus.
If the two-layer mat is led to a further scattering station, a further layer can initially be scattered with full width there in an analog manner by means of separating walls and subsequent, rotating separating units, with the excess particles subsequently being carried off in an unmixed state again to produce the desired reduced width and being fed to the metering hopper of the third scattering station for further use.
To achieve both the advantages with respect to the variable width adjustment and the alternative manufacture of chipboards, fiberboards or chip/fiber combination boards, the different apparatuses and methods described in the claims can be combined with one another as required.
Further advantageous embodiments of the invention are given in the dependent claims.